Mon, Jun 17, 2024 at 07:45:14AM CEST, chengen.du@xxxxxxxxxxxxx wrote: >The issue initially stems from libpcap. The ethertype will be overwritten >as the VLAN TPID if the network interface lacks hardware VLAN offloading. >In the outbound packet path, if hardware VLAN offloading is unavailable, >the VLAN tag is inserted into the payload but then cleared from the sk_buff >struct. Consequently, this can lead to a false negative when checking for >the presence of a VLAN tag, causing the packet sniffing outcome to lack >VLAN tag information (i.e., TCI-TPID). As a result, the packet capturing >tool may be unable to parse packets as expected. > >The TCI-TPID is missing because the prb_fill_vlan_info() function does not >modify the tp_vlan_tci/tp_vlan_tpid values, as the information is in the >payload and not in the sk_buff struct. The skb_vlan_tag_present() function >only checks vlan_all in the sk_buff struct. In cooked mode, the L2 header >is stripped, preventing the packet capturing tool from determining the >correct TCI-TPID value. Additionally, the protocol in SLL is incorrect, >which means the packet capturing tool cannot parse the L3 header correctly. > >Link: https://github.com/the-tcpdump-group/libpcap/issues/1105 >Link: https://lore.kernel.org/netdev/20240520070348.26725-1-chengen.du@xxxxxxxxxxxxx/T/#u >Fixes: 393e52e33c6c ("packet: deliver VLAN TCI to userspace") >Cc: stable@xxxxxxxxxxxxxxx >Signed-off-by: Chengen Du <chengen.du@xxxxxxxxxxxxx> >--- > net/packet/af_packet.c | 86 +++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 84 insertions(+), 2 deletions(-) > >diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c >index ea3ebc160e25..84e8884a77e3 100644 >--- a/net/packet/af_packet.c >+++ b/net/packet/af_packet.c >@@ -538,6 +538,61 @@ static void *packet_current_frame(struct packet_sock *po, > return packet_lookup_frame(po, rb, rb->head, status); > } > >+static u16 vlan_get_tci(struct sk_buff *skb, struct net_device *dev) >+{ >+ struct vlan_hdr vhdr, *vh; >+ u8 *skb_orig_data = skb->data; >+ int skb_orig_len = skb->len; >+ unsigned int header_len; >+ >+ if (!dev) >+ return 0; >+ >+ /* In the SOCK_DGRAM scenario, skb data starts at the network >+ * protocol, which is after the VLAN headers. The outer VLAN >+ * header is at the hard_header_len offset in non-variable >+ * length link layer headers. If it's a VLAN device, the >+ * min_header_len should be used to exclude the VLAN header >+ * size. >+ */ >+ if (dev->min_header_len == dev->hard_header_len) >+ header_len = dev->hard_header_len; >+ else if (is_vlan_dev(dev)) >+ header_len = dev->min_header_len; >+ else >+ return 0; >+ >+ skb_push(skb, skb->data - skb_mac_header(skb)); >+ vh = skb_header_pointer(skb, header_len, sizeof(vhdr), &vhdr); >+ if (skb_orig_data != skb->data) { >+ skb->data = skb_orig_data; >+ skb->len = skb_orig_len; >+ } >+ if (unlikely(!vh)) >+ return 0; >+ >+ return ntohs(vh->h_vlan_TCI); >+} >+ >+static __be16 vlan_get_protocol_dgram(struct sk_buff *skb) >+{ >+ __be16 proto = skb->protocol; >+ >+ if (unlikely(eth_type_vlan(proto))) { >+ u8 *skb_orig_data = skb->data; >+ int skb_orig_len = skb->len; >+ >+ skb_push(skb, skb->data - skb_mac_header(skb)); >+ proto = __vlan_get_protocol(skb, proto, NULL); >+ if (skb_orig_data != skb->data) { >+ skb->data = skb_orig_data; >+ skb->len = skb_orig_len; >+ } >+ } >+ >+ return proto; >+} >+ > static void prb_del_retire_blk_timer(struct tpacket_kbdq_core *pkc) > { > del_timer_sync(&pkc->retire_blk_timer); >@@ -1007,10 +1062,16 @@ static void prb_clear_rxhash(struct tpacket_kbdq_core *pkc, > static void prb_fill_vlan_info(struct tpacket_kbdq_core *pkc, > struct tpacket3_hdr *ppd) > { >+ struct packet_sock *po = container_of(pkc, struct packet_sock, rx_ring.prb_bdqc); >+ > if (skb_vlan_tag_present(pkc->skb)) { > ppd->hv1.tp_vlan_tci = skb_vlan_tag_get(pkc->skb); > ppd->hv1.tp_vlan_tpid = ntohs(pkc->skb->vlan_proto); > ppd->tp_status = TP_STATUS_VLAN_VALID | TP_STATUS_VLAN_TPID_VALID; >+ } else if (unlikely(po->sk.sk_type == SOCK_DGRAM && eth_type_vlan(pkc->skb->protocol))) { >+ ppd->hv1.tp_vlan_tci = vlan_get_tci(pkc->skb, pkc->skb->dev); >+ ppd->hv1.tp_vlan_tpid = ntohs(pkc->skb->protocol); >+ ppd->tp_status = TP_STATUS_VLAN_VALID | TP_STATUS_VLAN_TPID_VALID; > } else { > ppd->hv1.tp_vlan_tci = 0; > ppd->hv1.tp_vlan_tpid = 0; >@@ -2428,6 +2489,10 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev, > h.h2->tp_vlan_tci = skb_vlan_tag_get(skb); > h.h2->tp_vlan_tpid = ntohs(skb->vlan_proto); > status |= TP_STATUS_VLAN_VALID | TP_STATUS_VLAN_TPID_VALID; >+ } else if (unlikely(sk->sk_type == SOCK_DGRAM && eth_type_vlan(skb->protocol))) { >+ h.h2->tp_vlan_tci = vlan_get_tci(skb, skb->dev); >+ h.h2->tp_vlan_tpid = ntohs(skb->protocol); >+ status |= TP_STATUS_VLAN_VALID | TP_STATUS_VLAN_TPID_VALID; > } else { > h.h2->tp_vlan_tci = 0; > h.h2->tp_vlan_tpid = 0; >@@ -2457,7 +2522,8 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev, > sll->sll_halen = dev_parse_header(skb, sll->sll_addr); > sll->sll_family = AF_PACKET; > sll->sll_hatype = dev->type; >- sll->sll_protocol = skb->protocol; >+ sll->sll_protocol = (sk->sk_type == SOCK_DGRAM) ? >+ vlan_get_protocol_dgram(skb) : skb->protocol; > sll->sll_pkttype = skb->pkt_type; > if (unlikely(packet_sock_flag(po, PACKET_SOCK_ORIGDEV))) > sll->sll_ifindex = orig_dev->ifindex; >@@ -3482,7 +3548,8 @@ static int packet_recvmsg(struct socket *sock, struct msghdr *msg, size_t len, > /* Original length was stored in sockaddr_ll fields */ > origlen = PACKET_SKB_CB(skb)->sa.origlen; > sll->sll_family = AF_PACKET; >- sll->sll_protocol = skb->protocol; >+ sll->sll_protocol = (sock->type == SOCK_DGRAM) ? >+ vlan_get_protocol_dgram(skb) : skb->protocol; > } > > sock_recv_cmsgs(msg, sk, skb); >@@ -3539,6 +3606,21 @@ static int packet_recvmsg(struct socket *sock, struct msghdr *msg, size_t len, > aux.tp_vlan_tci = skb_vlan_tag_get(skb); > aux.tp_vlan_tpid = ntohs(skb->vlan_proto); > aux.tp_status |= TP_STATUS_VLAN_VALID | TP_STATUS_VLAN_TPID_VALID; >+ } else if (unlikely(sock->type == SOCK_DGRAM && eth_type_vlan(skb->protocol))) { I don't understand why this would be needed here. We spent quite a bit of efford in the past to make sure vlan header is always stripped. Could you fix that in tx path to fulfill the expectation? >+ struct sockaddr_ll *sll = &PACKET_SKB_CB(skb)->sa.ll; >+ struct net_device *dev; >+ >+ rcu_read_lock(); >+ dev = dev_get_by_index_rcu(sock_net(sk), sll->sll_ifindex); >+ if (dev) { >+ aux.tp_vlan_tci = vlan_get_tci(skb, dev); >+ aux.tp_vlan_tpid = ntohs(skb->protocol); >+ aux.tp_status |= TP_STATUS_VLAN_VALID | TP_STATUS_VLAN_TPID_VALID; >+ } else { >+ aux.tp_vlan_tci = 0; >+ aux.tp_vlan_tpid = 0; >+ } >+ rcu_read_unlock(); > } else { > aux.tp_vlan_tci = 0; > aux.tp_vlan_tpid = 0; >-- >2.43.0 > >
